1. Field of the Invention
The present invention relates to an interfacing apparatus having regular units, a spare unit, and a selector for replacing one of the regular units with the spare unit. In particular, the present invention relates to a line interfacing apparatus with an N+1 configuration employing N regular units and a spare unit applicable to an electronic exchange.
2. Description of the Related Art
A system with an N+1 configuration having N regular units and a spare unit is capable of continuing a normal operation even if one of the regular units fails by replacing the failed regular unit with the spare unit. To achieve this, a higher apparatus connected to the N+1-configuration system must have switches for the N regular units and spare unit and must identify a failed one among the regular units to run usual- and failure-operation programs. This puts a heavy load on the higher apparatus.
FIG. 1 shows a line interfacing apparatus 81 with an N+1 configuration for an electronic exchange according to a prior art. The apparatus 81 handles external lines (or relay lines) 88 and is connected to a higher apparatus 80 having a switching unit and to an opposite apparatus 89 through the lines 88. The lines 88 are divided into line groups 88-1 to 88-n each consisting of four lines in this example. The line groups 88-1 to 88-n are connected to terminating units 82-1 to 82-n (DT1 to DTn), respectively. Each of the terminating units has a multiplexer (MUX) for terminating and multiplexing the four lines. A multiplexed signal from each terminating unit is transmitted to a controller 87 through a channel 83. If one of the terminating units fails, a line selector (DTSW) 84 selects the line group connected to the failed terminating unit, and output lines of the line selector 84 are terminated and multiplexed by a spare terminating unit (MDT) 85. A multiplexed signal from the spare terminating unit 85 is transmitted to the controller 87 through a channel 86. The controller 87 has a multiplexer for multiplexing the multiplexed signals from the terminating units and a demultiplexer (DEMUX) for demultiplexing a multiplexed signal from the higher apparatus 80.
In this example, each of the line groups 88-1 to 88-n consists of four lines. For example, the line group 88-1 is made of lines 88-11 to 88-14 and the line group 88-n is made of lines 88-n1 to 88-n4. The line groups 88-1 to 88-n are connected to the terminating units 82-1 to 82-n, respectively and to the line selector 84. Each of the, terminating units 82-1 to 82-n has four relay contacts to connect and disconnect the four lines. For example, the terminating unit 82-1 has relay contacts RL011 to RL014 to connect and disconnect the lines 88-11 to 88-14, respectively, and the terminating unit 82-n has relay contacts RL0n1 to RL0n4 to connect and disconnect the lines 88-n1 to 88-n4, respectively. The line selector 84 has relay contacts RL111 to RL1n1 up to RL114 to RL1n4.
If one of the terminating units fails, the controller 87 opens the four relay contacts of the failed terminating unit and closes the relay contacts of the line selector 84 corresponding to the line group connected to the failed terminating unit. For example, if the terminating unit 82-1 (DT1) connected to the line group 88-1 fails, the controller 87 connects the line. group 88-1 to the spare terminating unit 85 through the line selector 84 and disconnects the line group 88-1 from the failed terminating unit 82-1.
Signals transmitted through the lines of each line group include main signals that are usually voice signals and control signals including subscriber status signals, select signals, and a failure notice signal. Each of the terminating units 82-1 to 82-n separately handles the main signals and control signals. Namely, each terminating unit multiplexes the main signals and control signals into separate multiplexed signals, which are transmitted to the higher apparatus 80 through separate channels. The spare terminating unit 85 has its own channels for main signals and control signals. If one of the terminating units fails, the failed terminating unit is switched to the spare terminating unit 85 through the line selector 84. At this time, the switching unit of the higher apparatus 80 must switch a path for the main signals passing through the failed terminating unit to a path passing through the spare terminating unit 85, and the controller 87 must handle control signals for the spare terminating unit 85 as control signals for the failed terminating unit.
In this way, the line interfacing apparatus of the prior art prepares a spare unit (the line selector 84 and spare terminating unit 85) for regular units (the terminating units 82-1 to 82-n). If one of the regular units fails, the prior art switches the failed unit to the spare unit while taking care of the switching of main signals, control signals, and failure signals. The prior art connects these signals to a higher apparatus through the regular and spare units. Namely, the spare unit always occupies some of signal channels between the interfacing apparatus and the higher apparatus, thereby deteriorating the efficiency of use of the signal channels.
When switching a regular unit to the spare unit, a higher controller installed in the higher apparatus sends a switching signal to the interfacing apparatus. Thereafter, control signals and a failure signal of the failed unit are replaced with those of the spare unit. The higher controller must correctly read these signals. To achieve this, the higher controller must manage the switching states of the regular and spare units, and once a regular unit fails and is switched to the spare unit, must identify the failed unit. The higher controller is usually controlled by software. The prior art requires a large software because the higher unit must switch line numbers for control signals not only for a maintenance program for handling the failed unit switching operation but also for a regular program for handling calls.
An object of the present invention is to provide a line interfacing apparatus with an N+1 configuration capable of improving the efficiency of use of channels between the interfacing apparatus and a higher apparatus.
Another object of the present invention is to reduce the size of software which operates a spare unit of the interfacing apparatus.
In order to accomplish the objects, the present invention provides a line interfacing apparatus with an N+1 configuration. The apparatus has N regular terminating units for terminating lines, respectively. Each of the regular terminating units has an end connected to an opposite apparatus through a corresponding one of the lines and another end connected to a higher apparatus having a switching unit. The interfacing apparatus further has at least one spare terminating unit, a line selector for selecting one of the lines and connecting the selected line to the spare terminating unit, and a termination controller having switches for switching channels between the regular and spare terminating units and the switching unit of the higher apparatus. If any one of the regular terminating units fails, the line selector is controlled to switch the line connected to the failed terminating unit to the spare terminating unit, and the switches of the termination controller are controlled to connect signals of the spare terminating unit, in place of signals of the failed terminating unit, to the switching unit of the higher apparatus.
With this arrangement, the line selector switches the line connected to the failed terminating unit to the spare terminating unit, and the output of the spare terminating unit is connected to an output channel of the failed terminating unit. As a result, channels for the spare terminating unit among channels for multiplexed signals between the interfacing apparatus and the higher apparatus are not always occupied. This improves the efficiency of use of channels.
Since the output of the spare terminating unit is connected to a terminal of the higher apparatus corresponding to the failed terminating unit, the higher apparatus is not required to have special software for reading the output of the spare terminating unit as the output of the failed terminating unit. This reduces load to form the software of the higher apparatus.